create documentation for API branching and deployment (#104)

<!-- Please complete the following sections as necessary. -->

### Description

This PR updates the `README` to include a `Branching` section so that it
is clear what the process is for getting a slice of work into production
for the Feedback Widget API.

### Ticket

<!-- Link to ticket in pivotal. Append ticket_id to provided URL. -->
This work resolves [Document Feedback Widget API Branch
Merging/Deployment
Process](newjersey/innovation-platform-pm#717).

### Approach

<!-- Any changed dependencies, e.g. requires an
install/update/migration, etc. -->
Updated the `README` to include a `Branching` section right
above`Deployment`.

### Steps to Test

<!-- If this work affects a user's experience, provide steps to test
these changes in-app. -->
N/A

### Notes

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considerations. -->
N/A

Author: AnJuHyppolite

README.md

@@ -18,6 +18,23 @@ For the latest information on the API endpoints maintained, see the functions im
 2. Run `npm install` (on Node 22, as listed in `.nvmrc`) to install Node dependencies
 3. Save the credentials from the `Innov-Platform-Dev` AWS account to your `~/.aws/credentials` file
 
+## Branching
+This repo has two primary branches: `dev` and `main`.
+
+### Branch and Environment Mapping
+- `dev` branch maps to the `Innov-Platform-Dev` AWS account
+- `main` branch maps to the `Innov-Platform-Prod` AWS account
+
+#### Workflow Steps
+1. Create a feature branch from the latest commit on `dev`.
+2. While working in a feature branch, if you need to deploy for testing, always deploy to the `Innov-Platform-Dev` account.
+3. Create PRs against the `dev` branch. Once a PR has been merged into `dev`, deploy the updated `dev` branch to the `Innov-Platform-Dev` account.
+4. Thoroughly test your changes in `dev` before deploying to the `Innov-Platform-Prod` account.
+   - At a minimum, you should test API requests to the dev API Gateway URL (see [Test API requests (non-browser)](https://github.com/newjersey/feedback-api?tab=readme-ov-file#test-api-requests-non-browser)) as well as [test API requests in the browser](https://github.com/newjersey/feedback-api?tab=readme-ov-file#test-api-requests-in-the-browser).
+   - Also, ensure that the expected changes to resources, etc. are visible in the AWS console.
+5. Once you've confirmed the dev deployment is working, merge `dev` into `main`.
+6. At this point, the changes are ready to be deployed to production. Make sure that you've checked out `main` and pulled the latest commits locally! Then, deploy the `main` branch to the `Innov-Platform-Prod` account.
+
 ## Deployment
 
 Deployment to AWS is done locally on the command line and is _not_ yet connected to Github version control.